Petroleum asphalt is produced as a residue of a thermal separation refinery process. The thermal separation process causes thermal cracking to occur which frequently causes hydrogen sulfide to be present in the asphalt stream. In fact, thermal cracking continues in the asphalt even after the asphalt has left the vacuum distillation section of the operation; particularly at high temperature. In order to permit the safe loading, handling, and storage of the asphalt, it is necessary to reduce the H.sub.2 S to safe levels in the asphalt. This has been done in the past by weathering of the hot asphalt for sufficient time for the H.sub.2 S to evolve. This not only takes a considerable amount of time (several days), but it releases H.sub.2 S to the vapor space in the storage which could create hazardous conditions. Moreover, recent emphasis on environmental regulations in Europe stresses the limits on the H.sub.2 S content of vent gas.
Other efforts to avoid these problems involve operating the vacuum distillation tower at a lower temperature to reduce thermal cracking in the residue. Lower temperature operation is achieved by increasing the flow of asphalt in a quench loop. This, however, is less efficient than operating at higher temperatures and decreases throughput and thermal recovery.
European Patent Specification, Publication No. 0121377 discloses the use of scavengers in treating bitumen/sulfur mixtures. The H.sub.2 S scavengers are used at temperatures between 130.degree. C. and 170.degree. C. to permit the mixing of sulfur and bitumen and to permit the safe handling of the mixture. Sulfur, in this application, is added to the bitumen to improve the end use properties of the bitumen. This publication does not relate to the production of asphalt or the treatment of freshly produced asphalt.